/*
 * FILE: resample.h
 *
 * The configuration constants below govern
 * the number of bits in the input sample and filter coefficients, the
 * number of bits to the right of the binary-point for fixed-point math, etc.
 *
 */
#ifndef _H_FASTRESAMPLE_
#define _H_FASTRESAMPLE_

typedef short          HWORD;
typedef unsigned short UHWORD;
typedef int            LWORD;
typedef unsigned int   ULWORD;

#define MAX_HWORD (32767)
#define MIN_HWORD (-32768)

/* Conversion constants */
#define Nhc       8
#define Na        7
#define Np       (Nhc+Na)
#define Npc      (1<<Nhc)
#define Amask    ((1<<Na)-1)
#define Pmask    ((1<<Np)-1)
#define Nh       16
#define Nb       16
#define Nhxn     14
#define Nhg      (Nh-Nhxn)
#define NLpScl   13

/* Description of constants:
 *
 * Npc - is the number of look-up values available for the lowpass filter
 *    between the beginning of its impulse response and the "cutoff time"
 *    of the filter.  The cutoff time is defined as the reciprocal of the
 *    lowpass-filter cut off frequence in Hz.  For example, if the
 *    lowpass filter were a sinc function, Npc would be the index of the
 *    impulse-response lookup-table corresponding to the first zero-
 *    crossing of the sinc function.  (The inverse first zero-crossing
 *    time of a sinc function equals its nominal cutoff frequency in Hz.)
 *    Npc must be a power of 2 due to the details of the current
 *    implementation. The default value of 512 is sufficiently high that
 *    using linear interpolation to fill in between the table entries
 *    gives approximately 16-bit accuracy in filter coefficients.
 *
 * Nhc - is log base 2 of Npc.
 *
 * Na - is the number of bits devoted to linear interpolation of the
 *    filter coefficients.
 *
 * Np - is Na + Nhc, the number of bits to the right of the binary point
 *    in the integer "time" variable. To the left of the point, it indexes
 *    the input array (X), and to the right, it is interpreted as a number
 *    between 0 and 1 sample of the input X.  Np must be less than 16 in
 *    this implementation.
*
 * Nh - is the number of bits in the filter coefficients. The sum of Nh and
 *    the number of bits in the input data (typically 16) cannot exceed 32.
 *    Thus Nh should be 16.  The largest filter coefficient should nearly
 *    fill 16 bits (32767).
 *
 * Nb - is the number of bits in the input data. The sum of Nb and Nh cannot
 *    exceed 32.
 *
 * Nhxn - is the number of bits to right shift after multiplying each input
 *    sample times a filter coefficient. It can be as great as Nh and as
 *    small as 0. Nhxn = Nh-2 gives 2 guard bits in the multiply-add
 *    accumulation.  If Nhxn=0, the accumulation will soon overflow 32 bits.
 *
 * Nhg - is the number of guard bits in mpy-add accumulation (equal to Nh-Nhxn)
 *
 * NLpScl - is the number of bits allocated to the unity-gain normalization
 *    factor.  The output of the lowpass filter is multiplied by LpScl and
 *    then right-shifted NLpScl bits. To avoid overflow, we must have
 *    Nb+Nhg+NLpScl < 32.
 */

typedef struct resampleContext {
	int	in_sample;	// input sample rate
	int	out_sample;	// output sample rate
	int	in_channels;	// input channels
	int	out_channels;	// output channels
	double	factor;		// out_sample / in_sample
	HWORD	*mid_buffer;	// middle buffer
	int	mid_bufsize;	// middle buffer size
} resampleContext;

int resampleFast(  	/* number of output samples returned */
    double factor,		/* factor = Sndout/Sndin */
    HWORD *inPtr,		/* input data pointer */
    HWORD *outPtr,		/* output data pointer */
    int inCount,		/* number of input samples to convert */
    int outCount,		/* number of output samples to compute */
    int nChans			/* number of sound channels (1 or 2) */
);

resampleContext *resampleContext_init(
    int in_channels, 		/* input channels 1 (mono), 2-stereo, -1: left, -2: right */
    int out_channels, 		/* ditto */
    int in_rate, int out_rate 	/* input and output sample rate */
);

void resampleContext_destroy( resampleContext *context );

void SND_resample( resampleContext *context,
	HWORD *iBuf, int inSize,
	HWORD *oBuf, int outSize
);

void SND_mixing( HWORD *audio, HWORD *audio_sum, int nsample );

#endif
